P0306 Chevy Silverado: Cylinder 6 Misfire Diagnosis and Fix

P0306 on a Chevy Silverado indicates a confirmed misfire in cylinder 6 — the third cylinder from the front on the passenger side of the engine. The diagnosis process is identical to all single-cylinder misfire codes, targeting the passenger-side bank.

Watch a cylinder-specific misfire traced to a failed ignition coil — the same plug, spark and coil checks apply to P0306.

What P0306 Means

The ECM detects cylinder 6 misfiring through crankshaft deceleration monitoring. Cylinder 6 is on the passenger side of the engine — if your P0306 diagnosis points to a bank-specific issue (lean condition, injector problem, or vacuum leak), focus on the passenger-side components.

Cylinder 6 Location

On all GM V8 engines: Passenger side front-to-rear = cylinders 2, 4, 6, 8. Cylinder 6 is the third cylinder from the front on the passenger side. This is an AFM deactivation cylinder on AFM-equipped 5.3L Silverados (2007–2021) — making lifter failure a specific risk at high mileage.

Common Causes

Failed ignition coil on cylinder 6 (most common), worn spark plug on cylinder 6, defective fuel injector, or on AFM trucks — failed AFM lifter on cylinder 6. Additionally, on GMT800 trucks, the passenger-side front of the engine has a coolant crossover passage — a leaking intake manifold gasket on the passenger side can contaminate cylinder 6 spark plug with coolant, causing a persistent misfire that won’t respond to coil or plug replacement alone. Check for white residue on the cylinder 6 plug if other diagnosis is clean.

Diagnosis

Step 1: Swap cylinder 6 coil to cylinder 8 position. If P0308 sets, replace the cylinder 6 coil. Step 2: Remove and inspect the cylinder 6 spark plug — look for fouling (carbon or oil), wet coolant residue (white/grey), or abnormal electrode wear. Step 3: On GMT800 trucks specifically, check for coolant in the intake — a sweet smell from the intake and white smoke at startup indicate manifold gasket issues. Step 4: If coil, plug, and injector are good, run a compression test on cylinder 6.

Related Codes

P0306 with a white-fouled plug on a GMT800 typically means intake manifold gasket failure — the infamous 1999–2001 GMT800 plastic intake manifold issue. See our GMT800 complete guide for details. For other misfire codes: P0300, P0304, P0305.